Tactile Situational Awareness Systems (TSASs) use an array of vibrating elements (typically vibrating motor or voice coil devices) called tactors, integrated into a vest to provide a pilot with spatial information. Using the sense of touch allows pilots to receive continuous spatial orientation information, even while visually attending to the aircraft instruments or external targets. Similar vibrotactile interfaces have been used to augment balance function in vestibular-impaired individuals, to aid in mapping responses in the somatosensory cortex, and have also been proven useful when vestibular and proprioceptive cues are entirely absent, such as the introduction of an artificial gravity vector in microgravity environments.
The main limitation preventing widespread adoption of the TSAS are the shortcomings of current tactor technology. An ideal TSAS vest would be light enough that a pilot can comfortably wear it during the standard preflight preparations. The vest should also have a large number of integrated tactors that are thin, robust, and deliver a powerful tactile signal. Current tactile display systems are unable to meet these requirements, often being too large or heavy, and are unable to deliver a powerful enough signal, especially when the vest is worn on the outside of a pilot's flight suit. These tactors often operate at a fixed resonant or drive frequency on a small skin contact area which leads to saturation of certain mechanoreceptors, decreasing their sensitivity to stimuli.
Psychophysical limitations of the human sensory system on the torso drive the specification for TSAS design and actuation. Humans can perceive a maximum of 3 levels of amplitude and 5 levels of frequency on the torso. Current TSAS implementations usually modulate a base frequency with lower frequency information signals, and drive the tactors at full amplitude to maximize tactile sensation. Base frequencies range from 40 Hz to 250 Hz, with pulse frequencies from 1 Hz to 4 Hz. For position limitations, users can only distinguish five tactors from waist to armpit.